Optimizing Designs of Integrated Circuits

ABSTRACT

Methods and systems for optimizing and/or designing integrated circuits. In one embodiment, a method for dynamically routing a net from equivalent resources is described, comprising identifying a critical load, determining whether a driver driving the critical load drives other components, and whether the critical load requires an improvement in slack, replicating the driver, to create a replicated driver, when the critical load requires an improvement in slack, coupling the replicated driver to the load; and tagging the replicated driver.

This application is a continuation of U.S. application Ser. No.14/229,753, filed on date Mar. 28, 2014, which is now U.S. Pat. No.9,208,281, issuing on Dec. 8, 2015, which is a divisional of U.S.application Ser. No. 13/007,579, filed on Jan. 14, 2011, which is nowU.S. Pat. No. 8,689,165, issuing Apr. 1, 2014, which is a divisional ofU.S. application Ser. No. 11/726,777, filed on Mar. 22, 2007, which isnow U.S. Pat. No. 7,873,930, issued Jan. 18, 2011. This application isalso related to and claims the benefit of the filing date of U.S.Provisional Patent Application No. 60/785,443, filed on Mar. 24, 2006,all of which applications are hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to the field of circuit design,and more particularly to automated circuit design synthesis through ahardware description language.

BACKGROUND

For the design of circuits on integrated circuits (ICs), designers oftenemploy computer aided design techniques. Standard languages known asHardware Description Languages (HDLs) have been developed to describecircuits to aid in the design and simulation of complex circuits.Several HDLs, such as VHDL and Verilog, have evolved as industrystandards. VHDL and Verilog are general purpose hardware descriptionlanguages that allow definition of a hardware model at the gate level,the register transfer level (RTL), or the behavioral level usingabstract data types.

In designing circuits using HDL compilers, designers first describecircuit elements in HDL source code and then compile the source code toproduce synthesized RTL netlists. The RTL netlists correspond toschematic representations of circuit elements. The circuits containingthe synthesized circuit elements are often optimized to improve timingrelationships and eliminate unnecessary or redundant logic elements.Such optimization typically involves substituting different gate typesor combining and eliminating gates in the circuit. FIG. 1 shows arepresentative flow for designing certain types of ICs, such as FieldProgrammable Gate Arrays (FPGAs) which have a predeterminedarchitecture, referred to as a target architecture. Operation 101involves receiving a description (e.g. a description written in HDL) ofan IC by a compiler which, in operation 103, performs a synthesis fromthe HDL description to an RTL description. In operation 105, the RTLdescription is mapped to a target architecture, such as the architectureof a Xilinx FPGA, and optimization within the target architecture isperformed. After optimization is completed, a netlist for the targetarchitecture is generated. Various methods and systems for computeraided design of ICs are described in U.S. Pat. Nos. 6,438,735;6,449,762; and 6,973,632, all of which are incorporated herein byreference.

FIG. 2 shows further details regarding a method, in the prior art, foroptimizing a design of an IC. In operation 151, the loads which aredriven by a particular component are determined, and in operation 153, amost critical load, of those loads, is determined. Then the particularcritical component is replicated (operation 155) and the most criticalload is connected (operation 157) to the replicated critical component.This will tend to reduce fanout at the source of the wiring net from theoriginal critical component. The load is considered critical if itadversely affects timing constraints or requirements for the IC (or ifit has negative slack), and the component is considered critical becauseit is driving the critical load. The slack of the IC is then recomputedin operation 159 and it is determined whether slack has improved(operation 161). If the slack has not improved, then the replication isdiscarded (operation 163) and processing returns to operation 151. Ifthe slack has improved, then processing returns from operation 161 tooperation 151 as shown in FIG. 2 to optimize other paths having othercritical components. FIGS. 3A, 3B, and 3C show an example of theoptimization method of FIG. 2.

FIG. 3A shows a representation of at least a portion of an integratedcircuit which may be designed according to the method of FIG. 1, with anoptimization performed according to the method of FIG. 2. The design atthis stage shown in FIG. 3A includes 9 switch matrices (SM) on therepresentation 201 of the integrated circuit. Switch matrices are commoninterconnection devices used on certain types of field programmable gatearrays, such as gate arrays from Xilinx. The switch matrices 202-210allow for the interconnection of various components, such as drivercomponents which output signals to loads which receive those signals.The design shown in FIG. 3A includes one driver 215 and 7 loads, L1-L7.In particular, driver 215 drives loads 216-222 through the routing netshown in FIG. 3A which includes wires W1, W2, and W3. The routing netincludes those three wires which are existing wire resources on the IC.The switches on the switch matrix 209 through which the wires areconnected are labeled SW1, SW2, and SW3, and the switch at the driver islabeled SWD. The critical loads in the design are L1, L2, L3 and L4 inthe order of criticality, most critical being first. The delay of thenet on each load depends on the wire delay, the switch delay and thefanout at each switch. The fanout at switch SWD is equal to 3 becausethere are 3 wires going to switches SW1, SW2, and SW3, which contributewith their capacitances to the wire delay. The total fanout of the netfrom driver D215 is equal to 7, but the root fanout at the switch SWD isonly 3. Further details showing the root fanout at switch SWD is shownin FIG. 3B which shows the driver component 215 providing an input tothe switch matrix 209 which is received by a driver 230 which in turndrives 3 pass gates (225, 226 and 227) in the switch SWD as shown inFIG. 3B. Each pass gate has a parasitic capacitance, an example of whichis shown as parasitic capacitance 231 on the pass gate 225. Theseparasitic capacitances add to the delay at the root fanout. It will beappreciated that the driver component 215 may be one of a variety ofdifferent logic components, such as a flip-flop, a lookup table or othertypes of logic, including digital logic circuits.

Previous methods for replication were concentrating at reducing thefanout, particularly the fanout at the root of the net, without payingattention at how the net is wired using existing wiring resources. Forexample, if we want to reduce the fanout by isolating the critical loadsL1 and L2, the driver D can be replicated and the copied driver 215A candrive the rest of the loads. The total fanout of the net driven from thedriver 215 will be 2 (down from 7) and the total fanout of the netdriven from driver 215A will be 5. This is depicted in FIG. 3C. However,in terms of delay, little will be changed for critical loads L3 and L4because the root delay of the net driven from driver 215A is still 3 asbefore replication, and the delay of the switch 254 and the wire W1Awhich is connecting loads L3 and L4 will be bigger if the faster wire W1was taken to connect to L1 and L2.

It is desirable to provide improved automated circuit design techniques,including techniques which include improved routing and optimizationtechniques which are described herein.

SUMMARY OF THE DESCRIPTION

The present inventions relate to various methods and apparatuses fordesigning an integrated circuit, and particularly to automated designusing a data processing system to design one or more integratedcircuits. According to one aspect of the present inventions, anexemplary method for designing an integrated circuit includes routing,at a first routing level as part of the process of designing the IC,connections on a representation of the IC using a first set of wiringresources and marking wiring resources as used once the wiring resourceswithin the first set have been used for routing and routing, at a secondrouting level using a second set of wiring resources in therepresentation of the IC, connections on the IC without checking whetherwiring resources within the second set have been previously used toroute connections, wherein wiring resources in the second set differ, onaverage, in physical size from wiring resources in the first set.Typically, the wiring resources in the second set are, on average,longer than wiring resources within the first set and the routing, whichuses the second set, is performed without marking wiring resourceswithin the second set as reserved once those wiring resources have beenused as part of a routing operation.

According to another aspect of the present inventions, an exemplarymethod includes determining a fanout of a driving component in arepresentation of the IC being designed, determining for the drivingcomponent the loads in the representation of the IC, driven by thedriving component, determining the use of existing wire resources usedto connect the loads to the driving component, and optimizing, based onthe use of existing wiring resources and the fanout of the drivingcomponent and the loads being driven by the driving component, a designof the IC. Typically, the optimizing includes determining whether toreduce fanout at the driving component by replicating the drivingcomponent, and the replicating is performed automatically by a dataprocessing system which is configured with a machine-readable medium toperform the replicating.

According to another aspect of the present inventions, an exemplarymethod includes determining, as part of a process of designing anintegrated circuit, a routing net from a load to a driving component anddetermining available places for a replicated version of the drivingcomponent, and creating, in the representation of the integratedcircuit, the replicated version of the driving component based on therouting net and the available places and creating connections, in therepresentation, between the replicated version and the load. This methodmay be used to perform load-based replication in which the replicationis performed by backtracking from a critical load through the availablewires and by examining available places for the replicated driver.Further, other critical loads in the area which may be driven by thesame replicated driver may also be connected through a progressiverouting method described below.

According to another aspect of the inventions described herein, anexemplary method includes replicating, as part of a process of designingan integrated circuit, a component in a representation of the IC andlabeling the component as a replicated component having an output whichis equivalent to an output of the component, and routing, in therepresentation, connections between the replicated component and theloads of the replicated component, and determining whether to use thereplicated component as a source to drive at least one existing load ofthe component. At least certain embodiments of this aspect allowrouting, in order to drive loads, from equivalent sources rather thanthe original source. By placing a tag on the replicated instancesthroughout the synthesis process, it is possible to identify equivalentsources which have been previously replicated so that routing operationsmay use those sources rather than an original source.

According to another aspect of the present inventions described herein,an exemplary method includes determining whether a value for a wiringdelay should be adjusted based upon a geometry of a wiring net in arepresentation of an integrated circuit being designed, and adjustingthe value if the geometry is of a first type, and determining routingdecisions, in the process for designing the integrated circuit, based onthe value after the adjusting. This exemplary embodiment may be used toadjust for characterized wiring delays, which may be either measured orestimated, based upon whether a particular long distance wiring net isprimarily a straight line through groups of switching matrices or astaircased path through another group of switching matrices.

The present inventions provide computer systems which are capable ofperforming various methods of the inventions, and the inventions alsoprovide computer readable media, such as machine-readable media, whichcontain executable program instructions which when executed by a dataprocessing system, such as a computer system, cause the data processingsystem to perform one or more of the methods described herein. Otherfeatures of the present invention will be apparent from the accompanyingdrawings and from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings in which likereferences indicate similar elements.

FIG. 1 is a flowchart which illustrates a process of HDL synthesis whichmay be used in at least certain embodiments of the present inventions.

FIG. 2 is a flowchart which shows a prior art method for optimizing adesign of an integrated circuit in an automated computer-aided designsystem.

FIG. 3A shows a representation of an integrated circuit during anautomated design process.

FIG. 3B shows further detail within the switching matrix of the designshown in FIG. 3A.

FIG. 3C shows the result of an optimization in the prior art performedaccording to the method shown in FIG. 2.

FIG. 4 is a flowchart which illustrates one exemplary embodiment of theinventions for performing an optimization of an integrated circuitdesign.

FIG. 5 shows a representation of an optimization resulting from oneembodiment of the method shown in FIG. 4.

FIG. 6 is a flowchart which illustrates a particular embodiment foroptimizing an integrated circuit design in which root fanout is reducedbased at least in part upon knowledge about the existing wiring netwhich is coupled to the root.

FIG. 7 is a flowchart which illustrates an exemplary embodiment ofanother aspect of the present inventions described herein.

FIG. 8 shows the layout of interconnections in at least certain types ofICs.

FIG. 9 is a flowchart which illustrates an exemplary method of a routingprocess according to certain embodiments of the present invention.

FIG. 10 is another flowchart showing a particular example of a routingprocess which is similar to the method shown in FIG. 9 and which may usethe architecture of an integrated circuit such as that shown in FIG. 8.

FIGS. 11A, 11B and 11C illustrate the process of designing a particularintegrated circuit in a sequence in time.

FIG. 12 is a flowchart which illustrates an exemplary method accordingto certain embodiments described herein, which method may produce thechanges shown in FIGS. 11A, 11B and 11C.

FIG. 13 shows an example of a layout of an integrated circuit having aplurality of switch matrices.

FIG. 14 is a flowchart which illustrates an exemplary method accordingto certain embodiments of the present invention which adjust wiringdelay based upon the geometry of a routing net, such as the twodifferent geometries shown in FIG. 13.

FIG. 15 is a block diagram of a data processing system, such as acomputer system, that may be used to implement one or more of theembodiments described herein and may include one or more forms ofmachine-readable media which store executable program instructions whichcause the data processing system to perform one or more of the methodsdescribed herein.

DETAILED DESCRIPTION

Methods and systems and machine-readable media for designing, through anautomated design process, an integrated circuit are described.

The subject invention will be described with reference to numerousdetails set forth below, and the accompanying drawings will illustratethe invention. The following description and drawings are illustrativeof the invention and are not to be construed as limiting the invention.Numerous specific details are described to provide a thoroughunderstanding of the present invention. However, in certain instances,well known or conventional details are not described in order to notunnecessarily obscure the present invention in detail.

Lead Fanout Reduction by Replication Based Upon Existing WiringResources

By utilizing information about the existing wiring sources whenreplication is performed to reduce fanout, such as fanout at the root ofa routing net, improved routing decisions and improved results may beachieved as shown in FIG. 5 relative to FIG. 3C. In particular, bytaking into account the existing wiring resources before replicating thedriver 215, it may be decided that critical loads L1, L2, L3 and L4should be connected with wire W1 from the driver D (driver 215) and thatthe rest of the loads are driven from the replicated copy of driver D,which is shown as driver 311 in FIG. 5. The root fanout at the switchSWD is still 1, because the loads L1-L4 are driven with the same wireW1. The root fanout at the replicated copy of the driver 311 is reducedby 1, so other loads driven by the driver 311 will have a better netdelay due to the reduction of root fanout at the replicated driver. Thecritical loads L1-L4 will have improvement in net delay from theoriginal netlist shown in FIG. 3A, resulting in improvement in 4different paths compared to only improvement in only 2 critical paths asshown in FIG. 3C.

FIG. 4 shows a general method for performing routing operations usinginformation about the routing tree when replicating drivers either at aroot fanout location or at an intermediate fanout location throughout arouting net. Operation 301 includes determining, for a critical driver,such as the driver 215, the critical loads which are driven by thecritical driver. This typically involves determining whether certainloads are critical loads and then determining the drivers which drivethose critical loads. Those drivers are critical drivers because theydrive the critical loads. The loads are critical because, for example,they affect timing constraints or requirements. For example, a load maybe critical if a slack measurement at a particular load output isnegative or not positive enough. In the case of the design shown in FIG.5, the loads L1-L4 are critical loads which are driven by the criticaldriver 215. Operation 301 of course performs this determination based onthe original design before this optimization, and thus the integratedcircuit shown in FIG. 3A is used in operation 301 to determine, for thecritical driver 215, which loads are critical. Then, using the sameunoptimized design, operation 303 determines information about therouting tree which connects the critical driver to all of its loads.Thus, in the case of the design shown in FIG. 3A, operation 303determines information about the routing tree which connects thecritical driver 215 to all 7 of the loads L1-L7. Then in operation 305,the routing tree is optimized from the critical driver using theinformation about the loads and using the information about the routingtree. Hence, the optimization process considers the actual existingwiring resources which are used to couple the critical driver 215 to itsvarious loads when determining how to replicate the driver and how toroute the replicated driver and the original driver relative to theoriginal loads. Thus the optimization process in operation 305 changesthe design shown in FIG. 3A to create the design shown in FIG. 5 inwhich the replicated driver 311 has a reduced fanout and drives allloads except the critical loads, while the original driver 215 continuesto use the same routing net shown in FIG. 3A and has a reduced rootfanout. As noted previously, this method may be performed to reduce rootfanout for all critical drivers in a design and may optionally be usedto perform a reduction of fanout at intermediate drivers throughout arouting tree. This method may be performed by using techniques known inthe field of operations research to achieve optimal or near optimalrouting using information about the loads, the driver(s) and also theactual existing wiring resources which couple the loads to the driverand which can be used to couple to new drivers created throughreplication. The parameter which is optimized by the operation researchtechniques may be timing.

FIG. 6 is a flowchart which illustrates one particular example in whichthe method of FIG. 4 may be performed to optimize a design of anintegrated circuit by reducing root fanout from a driver, which in thecase of FIG. 6 is assumed to be a critical driver or component. It willbe appreciated that “driver” or “component” refers to logic elements,such as flip-flops or lookup tables or other digital logic componentswhich generate signals which in turn are outputted to other componentswhich receive those signals as inputs to the other components. Themethod of FIG. 6 begins in operation 351 in which it is determined, fora particular critical component, which loads are driven by thatparticular critical component. In operation 353, the routing net tree iscomputed or determined for each net driven by the particular criticalcomponent. For example, the fanouts at each branch point in that routingtree are determined, and it is determined which nodes are critical ornon-critical on the net. Then in operation 355, after gatheringinformation about the actual routing tree, a replicated driver, which isa replicated version of the particular critical component, is createdfor all critical loads on one branch of the routing net tree, and thisreplicated driver is used to drive those loads. Alternatively, theoriginal driver may be used to drive those loads on the one branch ofthe routing net tree and a replicated driver, which is a replica of theparticular critical component, is used to drive all other loads of therouting net tree. This alternative is what was performed to create thedesign of FIG. 5 in which the original driver 215 was kept in its placeto drive the 4 critical loads while a replicated driver 311 was used todrive, through a modified routing net tree, the remaining loads. Inoperation 357, the critical loads are connected to the replicated driverand then in operation 359, slack is recomputed. If slack is determined,in operation 361, to have improved, then the method returns, throughoperation 365, to attempt to optimize other routing nets by repeatingthe operations shown in FIG. 6, beginning again from operation 351. Ifslack has not been improved as determined in operation 361, then thereplication is discarded in operation 363 and processing returns tooperation 351 to attempt to optimize the design in other ways.

Load-Based Replication

Load-based replication is performed when there is a small number ofcritical loads on a net. A dedicated copy for each load is created. Inan example shown in FIG. 3A, if loads L3 and L4 were not critical, thencreating a copy of a driver for only L1 and L2 is a good solution. Inthe case of a flip-flop as a driver, the driver can be placed in closeproximity to the loads and the loads are connected to the fastestpossible wire. In performing load-based replication, the process beginsfrom the load side and examines the routing net by backtracking from theload through the available existing wires to the driver. This processcan also take into account available locations for placement of thereplicated driver in the process of backtracking through the existingwiring net. Further, the process may evaluate whether other criticalloads driven by the same driver are also present in the same area anduse the progressive routing techniques described below to connect theother critical loads also to the replicated driver. This is unlike priorsolutions which would just replicate the driver for a particularcritical load and then connect that replicated driver to the criticalload. A version of this load-based replication process is shown in FIG.7. It will be appreciated that the method shown in FIG. 7 is part of anoptimization process, such as the optimization process shown inoperation 105 of FIG. 1. The method of FIG. 7 may begin in operation 401in which a critical load is selected for possible load-basedreplication. In operation 403, the routing net from that critical loadis determined back to the original driver and it is also determined whatplaces are available for a new copy of that original driver. Then inoperation 405, based upon the routing net and the available places forthe replicated copy, the method creates a replicated driver and connectsit to the selected critical load. The method may then continue inoperation 407 by examining other critical loads in the same routing netfrom the original driver in the vicinity of the selected critical loadand decide whether or not to connect those other critical loads to thereplicated driver.

Progressive Routing

FIGS. 8, 9, and 10 relate to a method for performing routing operationswhich may be performed after placement operations or concurrently withplacement operations. This routing technique will often produceacceptable IC designs faster than prior art techniques because theruntime of the compiler used to synthesize and optimize a design isoften improved by using the progressive routing technique describedherein. This technique may utilize characterized wiring delays in aparticular IC architecture, and these characterized wiring delays may beactually measured wiring delays or predicted or estimated wiring delaysbased on knowledge with respect to a particular chip architecture.

The particular chip architecture is also referred to sometimes as atarget architecture, which is typically determined by a supplier of theprogrammable integrated circuits. An example of a target architecture isthe programmed lookup tables and associated logic of certain integratedcircuits available from Xilinx, Inc. of San Jose, Calif. Other examplesof target architectures include those well-known architectures in fieldprogrammable gate arrays and complex programmable logic devices fromvendors such as Altera, and others.

FIG. 8 shows an example of a particular IC architecture which utilizesan array of switching matrices, which are similar to the switchingmatrices shown in FIGS. 3A and 3B. These switching matrices areconnected by existing wiring resources which are available to be usedbetween the different switch matrices. The switches within the switchmatrices may or may not connect, after the design is completed, to thesevarious existing wiring resources. The architecture of the integratedcircuit 451 shown in FIG. 8 includes switch matrices 452-459 which arecoupled by what may be characterized as 3 different sets of wiringresources based upon a physical size, on average, of a wiring resourcewithin one set of wiring resources. In particular, wires 461A, 461B,461C, and 461D may be considered part of a first set of wiring resourcesbecause the length, on average, of those wiring resources is smallerthan the length of other wiring resources shown in FIG. 8. Further, thewiring resources 461E and 461F may also be considered part of the firstset of wiring resources given their short length. A longer set of wiringresources, and hence a second set of wiring resources, may includewiring resources 463A, 463B, 463C, and 463D. These wiring resources maybe considered an intermediate wiring resource or set of wiring resourcesbecause their length is less than longer wiring resources but more thanshorter wiring resources in the first set of wiring resources. The thirdset of wiring resources, which is the longest set of wiring resourcesshown in FIG. 8, includes wiring resources 465A, 465B, and 465C. Thesewiring resources are longer than any other wiring resource shown in FIG.8. It will be appreciated that the integrated circuit represented byFIG. 8 may be larger and that there are further switch matrices notshown, and it will also be appreciated that additional wiring resources,which are not shown, are used to interconnect the switch matrices whichare shown. These additional wiring resources have not been shown inorder to simplify FIG. 8.

The three sets of wiring resources may each be used to define howrouting is performed and how delay through the routing net is estimated.In the case of FIG. 8, each set is defined based on the distance the nethas to be routed across. The first set is for nets spanning the shortestdistance, and in the process of routing those nets, wiring resources aretracked as they are used. There is a finite, small number of wires thatconnect from end to end of a short run. When such a net is routed, thewires used by a route which has been completed are marked as reserved,and before subsequent routes are completed, the method checks todetermine whether a wiring resource is available (which can bedetermined by seeing whether a wiring resource has been marked asreserved or is no longer listed on an available list of wiringresources). The shorter wiring distance typically means that the delaythrough the wiring net is more accurate and may be obtained fromactually measuring the wire or predicting the wiring delay based uponthe physical structure of the wires on a particular integrated circuit.In the Xilinx FPGA Virtex family of integrated circuits, the first setof wiring resources is defined on a 5×5 CLB box, because these are theshortest, fastest wires that connect pins on that distance. The secondset of wiring resources is defined for a distance which is bigger thanthe, on average, shorter distance of the first wiring resources. Forexample, the second set of wiring resources may be for a net which canbe routed with 2 or more short wires. While this particular example isnot shown in FIG. 8, certain IC architectures allow for a switch matrixto interconnect two short wires to create a longer wire. In this secondset of wiring resources, the delay of the net is estimated but, asdescribed below, the wire resources are not reserved as they are used inthe routing process. This is an acceptable practice because there aremore choices of wires to use in the routing process over longerdistances. The delay prediction is still accurate because several wirechoices lead to similar net delays, and the relative error in delayprediction is small. In the Xilinx FPGA Virtex family, this set ofwiring resources is defined on a 13×13 box. The predicted delay may beobtained from point-to-point delays within this box, and the values forthe delay may be stored in a lookup table. The third set of wiringresources may be for distances which are bigger than the second set andwhich can span the whole chip. For this set of wiring resources, anestimator with statistical detour analysis may be used to estimate thewiring delays.

FIG. 9 shows a general example of a method of routing whichdistinguishes between groups or sets of wiring resources based upon adifference, on average, in physical size between the wiring resources ineach set. The method of FIG. 9 may be performed after placement ofcomponents in a representation of an integrated circuit during anautomated design process or concurrently with placement as shown inoperation 501. In operation 503, short routes, which will be marked asreserved, are defined in operation 503. In the example of FIG. 8, thewiring resources 461A-461F are defined as short routes which will bemarked as reserved after performing a routing operation which uses oneor more of those wiring resources. In operation 505, long routes aredefined which will not be reserved when routing and placing is performedand hence the routing process does not check for any reservations oflonger routes while doing the routing using the longer routes. This, ofcourse, raises the possibility that some routes are used two or moretimes because no effort was made to check whether a particular longroute had previously been used to route a connection through. In theexample of FIG. 8, the wiring resources 463A-463D are an example of aset of long routes which are defined by operation 505. After routing andplacing is initially completed, then an examination, in operation 507,is performed to determine whether there is any duplicate use of thelonger routes which were not marked as reserved when performing therouting operations. It is anticipated that the software operations whichare necessary to perform operation 507 will consume less time than thesoftware operations which are required to mark used routes as reservedand then to check, when doing subsequent routing, whether a wiringresource has previously been used. In other words, it is anticipatedthat routing operations will be faster by ignoring whether prior routingoperations for longer routes have used certain routes than in actuallychecking, when doing longer routes, whether prior routing operationshave used any of the longer routes. If there are duplicate uses oflonger routes, then in operation 509, the method corrects thoseduplicate uses by routing each of the duplicated uses through anotherpath; preferably signals having the largest positive slack are selectedfor rerouting to avoid duplicate uses.

FIG. 10 shows a more detailed example of a method of progressiverouting, which is similar to the method shown in FIG. 9 and may beemployed in an architecture such as that shown in FIG. 8. The method ofFIG. 10 begins in operation 551 in which the wire delays arecharacterized for at least a set of interconnects, such as the shortinterconnects of an integrated circuit. In the example of FIG. 8, theinterconnects between switch matrices and a field programmable gatearray are characterized by either actually measuring those delays or byestimating or predicting those delays. In operation 553, routing of theshort connections, which have been characterized, is performed bydetermining routing between a driver and the loads for that driver. Ineach case, as a route is performed, it is marked as reserved so thatsubsequent routings for short connections can check whether or not adesired route, before it is used, has been previously used. The previoususe is shown by whether or not it has been reserved. It will beappreciated that in alternative embodiments, a list of available routingresources may be maintained and once a routing resource is used, it isremoved from the list so that subsequent routing operations, beforefinishing a routing operation, can check that list to determine whetheror not the wiring resource is available depending on whether or not itis on the list. This may be considered to be another way of reserving orshowing that a wiring resource has been used in a routing operation. Inoperation 555, the intermediate connections, which may be characterized,are routed, but these routing operations are performed without anymarking of reservations for the routed intermediate connections, and sosubsequent routings for intermediate connections are performed withoutchecking to see if the desired route has been previously reservedbecause it has been used in a prior routing operation. In operation 557,routing of long connections is then performed by determining the routingof those long connections and doing so without any reservations andwithout checking to see if a desired route has already been used, asshown by a marked reservation by a prior routing operation. Finally, inoperation 559, after routing and placing is initially completed, a checkis performed for duplicate uses of the same routes and those duplicateuses are corrected as described above.

Routing from Equivalent Resources

FIGS. 11A, 11B, and 11C, and FIG. 12, relate to a method for routingfrom equivalent resources. Using this method, when a net needs to berouted, the system can dynamically route from any equivalent source ofthis net, such as a replicated instance of a driver which is the driverof all nodes for a particular net. The method shown in FIG. 12 will beused relative to the circuits shown in FIGS. 11A, 11B and 11C todescribe one particular method for routing from equivalent sources. Thismethod may be performed on optimization or whenever performingreplication. Furthermore, this method may be used whenever placingobjects, such as replicated objects, or when moving those objects aroundwhen attempting to optimize the design of an integrated circuit. Inoperation 701, it is decided whether or not to replicate a particularcomponent. In the case of the circuit shown in FIG. 11A, the decision ismade whether or not to replicate the driver 601 which currently drives,as shown in FIG. 11A, 3 loads L1, L2 and L3 in the array of 6 lookuptables 604 and load L5 in another part of the integrated circuit as wellas a critical load L4 605. Because critical load L4 requires animprovement in slack, it is decided to replicate the driver 601, whichhas its output signal A driven to the 5 loads as shown in FIG. 11A. Thereplication operation is performed, resulting in the circuit shown inFIG. 11B in which the driver 601 is now replicated to create areplicated driver 601A which produces, at its output, A′ which isequivalent to or the same as the output from the driver 601. This newreplicated driver is coupled through a switch matrix 609 to the load605. The driver 601 continues to drive the loads L1, L2 and L3 throughthe switch matrix 603 and also continues to drive the load L5. Thedesign shown in FIG. 11B is an improvement over the design shown in FIG.11A at least because of the fact that root fanout at the entrance to theswitch matrix 603 has been reduced for the driver 601 and the load 605now has its own dedicated driver which is a replicated copy of thedriver 601. As shown in operation 703, when the component is replicated,it is labeled as a replicated component showing that it has anequivalent output of the equivalent component which was replicated. Thistag permits the system to identify replicated components as beingequivalent to the original component when routing and moving componentsaround in the process of optimizing the design of an integrated circuit.The design shown in FIG. 11B is the result of operation 705 in which thereplicated component has been placed in the design and the connectionshave been routed between the replicated component, in this case thedriver 601A, and the load 605. In the process of continuing to optimizethe routing and/or placement of components, it is determined whether, inoperation 707, to use a replicated component as a source to drive someloads of the original component. For example, as the system places androutes during an optimization process, it can automatically determinewhether to route a connection to a load from the component currentlyassigned to drive it or from another equivalent source of the signalfrom the component. The result of this operation and operation 709 isshown in FIG. 11C in which the load L5 is also coupled to the replicateddriver 601A because it is an equivalent source to the driver 601. Thisproduces a result in which the root fanout of the driver 601A is reducedto 3 and a potentially shorter routing resource is made available todrive the load L5 without potentially significantly impacting thedriving of the load 605. The method of FIG. 12 may be performed whenplacing or moving components and gives a “placer” greater flexibility inplacing objects around the design of the integrated circuit asequivalent sources for driving those loads can now be utilized.

Adjustment for Routing Geometry

FIGS. 13 and 14 relate to an aspect of the present inventions in whichcharacterized wiring delays are adjusted based upon the geometry of thewiring net. In at least certain chip architectures, it has been observedthat the wiring delay through a substantially horizontal orsubstantially vertical wiring path may be slightly longer thananticipated relative to a wiring path which is substantially diagonal orstaircased. The difference between these two geometries in routing netsis shown in FIG. 13. The routing net between driver D2 (driver 819) andload L2 (load 821) is a substantially horizontal routing path. On theother hand, the routing path between driver D1 and load L1 (driver 815and load 817) is along a substantially diagonal path on the integratedcircuit 801. This integrated circuit includes 9 switch matrices 802-810which serve to allow loads and drivers to be interconnected across theintegrated circuit. The wiring delay between switch matrices in either ahorizontal or diagonal direction or a vertical direction may becharacterized as shown in operation 851. This characterization may be anactual measurement of timing delays between adjacent or several switchmatrices along a row or along a diagonal path or substantially diagonalpath. The characterization may also be performed using predictions orestimates rather than actual measurements. In operation 853 it isdetermined, for a long wiring net, whether the characterized wiringdelay needs to be adjusted based upon the geometry of the net. Forexample, it is determined whether a long wiring net will be mostly alonga straight line, such as a horizontal or vertical line, or mostly alonga staircased path, such as the path taken by the wiring net whichcouples the driver 815 to the load 817. If it is in fact determined inoperation 853 that the wiring delay, which has been characterized, needsto be adjusted, then it is adjusted in operation 855 and then routingdecisions are determined based upon the adjusted wiring delay inoperation 857.

The adjustment of the timing delay can be performed dynamically asobjects are moved or placed around the different switch matrices. Thedetermination of whether the characterized wiring delay needs to beadjusted may be performed by calculating a probability that a particularnet will not be wired along a horizontal line but by segments ofhorizontal and vertical lines going toward the load. This jogprobability can be computed by statistically taking into account thewires that are already used on a particular portion of the path, andthis probability can be calculated before completing the routingoperation between the load and the driver. It can be taken into accountfor a design (or statistically computed for a collection of designs) thedistribution of the number of drivers that have loads on a horizontal orvertical line. The routing architecture has a limited number ofhorizontal and vertical routing resources, so not all loads can berouted using a direct wire. Instead, the wiring for some loads will takea detour from the horizontal or vertical line. The probability of thatdetour is computed based on the number of horizontal or vertical wiresand the distribution of the number of loads for drivers in a design(example 20 cells have 7 loads, 30 cells have 10 loads, etc.).Consequently, additional wiring delay is added to all long wires basedon this jog probability.

Data Processing System

FIG. 15 shows a block diagram of a computer system which may be used toimplement an embodiment of the present invention. The computer systemmay include one or more machine-readable media which store executablecomputer program instructions which when executed by the data processingsystem, such as the computer system, causes the computer system toperform one or more of the methods described herein. The computer systemmay, for example, be used to perform the progressive routing methoddescribed herein as part of a synthesis of an integrated circuit. Thecomputer system includes a processor 902 which is coupled through a bus901 to a random access memory 904, a read-only memory (ROM) 906 and amass storage device 907. The mass storage device 907 represents apersistent data storage device, such as a floppy disk drive, a fixeddisk drive or other non-volatile storage mechanisms, such as flashmemory. The processor 902 may be embodied in a general purposeprocessor, such as an Intel Pentium processor or a special purposeprocessor or a specially programmed logic device. Display device 920 iscoupled to processor 902 through bus 901 and provides graphical outputfor the computer system 900. Keyboard 921 and cursor control unit 922are coupled to the bus 901 for communicating information and commandselections to the processor 902. Also coupled to the processor 902through bus 901 is an input/output interface 123 which can be used tocontrol and transfer data to electronic devices, such as printers, othercomputers, etc. which are connected to the computer system 900. Itshould be noted that the architecture of the computer system shown inFIG. 15 is provided only for purposes of illustration, and that acomputer used in conjunction with the present inventions is not limitedto this specific architecture.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will be evidentthat various modifications may be made thereto without departing fromthe broader spirit and scope of the invention as set forth in thefollowing claims. The specification and drawings are, accordingly, to beregarded in an illustrative sense rather than a restrictive sense.

What is claimed is:
 1. A method for dynamically routing a net fromequivalent resources, comprising: identifying a critical load;determining whether a driver driving the critical load drives othercomponents, and whether the critical load requires an improvement inslack; replicating the driver, to create a replicated driver, when thecritical load requires an improvement in slack; coupling the replicateddriver to the load; and tagging the replicated driver.
 2. The method ofclaim 1, wherein the replicated driver is coupled through a switchmatrix.
 3. The method of claim 1, wherein the tagging permits the systemto identify replicated components as being equivalent to the originalcomponent when routing and moving components around in the process ofoptimizing the design of an integrated circuit.